Manufacture of xylenes using reformate

ABSTRACT

A process is provided for the production of xylenes from reformate. The process is carried out by methylating under conditions effective for the methylation, the benzene/toluene present in the reformate outside the reforming loop, to produce a resulting product having a higher xylenes content than the reformate. Greater than equilibrium amounts of para-xylene can be produced by the process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/465,058filed Jun. 18, 2003, now U.S. Pat. No. 7,176,339, which claims priorityto U.S. Provisional Application No. 60/389,977 filed Jun. 19, 2002 andis fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for producing xylenes usingreformate by methylating the benzene and/or toluene contained in thereformate to produce xylenes.

2. Description of the Prior Art

Most aromatics production is based on the recovery of aromatics derivedfrom catalytic reforming of naphtha. That process, using a feedcontaining a C₆₊ hydrocarbons, typically produces a reformate comprisedof C₆-C₈ aromatics along with paraffins and heavier aromatics.

Aromatics can also be produced by the dehydrocyclo-oligomerization ofC₂-C₅ aliphatic hydrocarbons. That process typically produces a productcomprised of benzene, toluene, xylenes, C₅₊ paraffins, C⁴⁻ lightparaffins, olefins, and unreacted C₂-C₅ aliphatic hydrocarbons.

Another technique for producing aromatics involves the cracking ofhydrocarbons such as by steam cracking or catalytic cracking. Thatprocess typically produces a product comprised of benzene, toluene,xylenes, C₆₊ paraffins, and other hydrocarbons.

The aromatics present in the reformate stream from a reformer or crackerwill depend on the composition of the feedstock to the reformer orcracker, the type of reformer or cracker, and the operating conditionsof the reformer or cracker. Normally, the aromatics present in thereformate stream will comprise benzene, toluene, a near equilibriummixture of xylenes, ethylbenzene, and a mixture of nominally of C₉-C₁₀.Products of the reformate having the most value are benzene and xylenes.Of the xylene isomers, i.e., ortho-, meta- and para-xylene, thepara-xylene is of particular value as a large volume chemicalintermediate in a number of applications, such as the manufacture ofterephthalic acid, which is an intermediate in the manufacturer ofpolyester.

The reformate is usually sent to an aromatics recovery complex where itundergoes several processing steps in order to recover high valueproducts, e.g., xylenes and benzene, and to convert lower valueproducts, e.g., toluene, into higher value products. For example, thearomatics present in the reformate are usually separated into differentfractions by carbon number; e.g. benzene, toluene, xylenes, andethylbenzene, etc. The C₈ fraction is then subjected to a processingscheme to make more high value para-xylene. Para-xylene is usuallyrecovered in high purity from the C₈ fraction by separating thepara-xylene from the ortho-xylene, meta-xylene, and ethylbenzene usingselective adsorption or crystallization. The ortho-xylene andmeta-xylene remaining from the para-xylene separation are isomerized toproduce an equilibrium mixture of xylenes. The ethylbenzene isisomerized into xylenes or is dealkylated to benzene and ethane. Thepara-xylene is then separated from the ortho-xylene and the meta-xyleneusing adsorption or crystallization and the para-xylene-deleted-streamis recycled to extinction to the isomerization unit and then to thepara-xylene recovery unit until all of the ortho-xylene and meta-xyleneare converted to para-xylene and recovered.

Toluene is typically recovered as a separate fraction and then may beconverted into higher value products, e.g., benzene and/or xylenes. Onetoluene conversion process involves the disproportionation of toluene tomake benzene and xylenes. Another process involves the hydrodealkylationof toluene to make benzene.

Both toluene disproportionation and toluene hydrodealkylation result inthe formation of benzene. With the current and future anticipatedenvironmental regulations involving benzene, it is desirable that thetoluene conversion not result in the formation of significant quantitiesof benzene.

Xylenes can be produced by the methylation of toluene. Such a process isdisclosed in U.S. Pat. No. 3,965,207. One advantage of producing xylenesby this process is that the xylenes production does not result in theformation of benzene by-product.

The recovery of toluene from reformate as a separate fraction requiresseveral processing steps. Typically, after removal of hydrogen and theC₁-C₅ and C₈₊ fractions, the C₆-C₇ aromatics (benzene and toluene) areseparated from the C₆-C₇ paraffins by aromatics extraction. The tolueneis then separated by distillation from the benzene and then sent to atoluene methylation unit to undergo toluene methylation to producexylenes. A problem associated with this technique is that the aromaticsextraction step can add significantly to the cost of producing ofxylenes via toluene methylation. Also, a bottleneck condition can occurif the extraction capacity of the aromatics extraction unit does notaccommodate the reaction capacity of the toluene methylation unit.Further, separation of toluene from reformate as a separate fraction mayrequire substantial capital investment in additional equipment, e.g.,benzene/toluene recovery unit and xylenes recovery unit etc.

The present invention is directed to a process for producing xylenesusing reformate by toluene methylation which overcomes or at leastmitigates one or more of the above-described problems.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a processfor producing xylenes using reformate, which process comprises:

-   -   (a) providing a reformate containing hydrogen, C₁-C₅        hydrocarbons, C₆-C₇ hydrocarbons comprising benzene, toluene or        mixtures thereof, and C₈₊ hydrocarbons;    -   (b) removing at least a portion of said hydrogen from said        reformate to produce a product having less hydrogen content than        said reformate; and    -   (c) methylating at least a portion of the benzene, toluene, or        mixtures thereof present in said product in a methylation        reaction zone with a methylating agent under conditions        effective for the methylation and in the presence of a catalyst        effective for the methylation to produce a resulting product        having a higher xylenes content than said reformate.

In the practice of the present invention according to theabove-described embodiment, usually at least a portion of the C₁-C₅hydrocarbons present in the reformate is removed before methylationtakes place.

In another embodiment, the present invention provides a process forproducing xylenes using reformate formed in an aromatization zone, whichprocess comprises the step of:

-   -   (a) providing a reformate containing hydrogen, C₁-C₅        hydrocarbons, C₆-C₇ hydrocarbons comprising benzene, toluene or        mixtures thereof, and C₈₊ hydrocarbons;    -   (b) removing at least a portion of said hydrogen from said        reformate to produce a first product having less hydrogen        content than said reformate;    -   (c) removing at least a portion of said C₁-C₅ hydrocarbons from        said first product in a C₁-C₅ hydrocarbon separation zone to        produce a second product having less C₁-C₅ hydrocarbon content        than said first product;    -   (d) removing at least a portion of said C₈₊ hydrocarbons from        said second product in a C₈₊ hydrocarbon separation zone to        produce a third product having less C₈₊ hydrocarbons content        than said second product;    -   (e) transferring at least a portion of said third product to a        methylation reaction zone; and,    -   (f) methylating in said methylation reaction zone at least a        portion of the benzene, toluene, or mixtures thereof present in        said third product with a methylating agent under conditions        effective for the methylation and in the presence of a catalyst        effective for the methylation to produce a fourth product having        a higher xylenes content than said reformate.

In a further embodiment, the present invention provides a process forproducing xylenes using reformate formed in an aromatization zone, whichprocess comprises the step of:

-   -   (a) providing a reformate containing hydrogen, C₁-C₅        hydrocarbons, C₆-C₇ hydrocarbons comprising benzene, toluene or        mixtures thereof, and C₈₊ hydrocarbons;    -   (b) removing at least a portion of said hydrogen from said        reformate to produce a first product having less hydrogen        content than said reformate;    -   (c) removing at least a portion of said C₈₊ hydrocarbons from        said first product in a C8+ hydrocarbon separation zone to        produce a second product having less C₈₊ hydrocarbon content        than said first product;    -   (d) transferring at least a portion of said second product to a        methylation reaction zone; and,    -   (e) methylating in said methylation reaction zone at least a        portion of the benzene, toluene, or mixtures thereof present in        said second product with a methylating agent under conditions        effective for the methylation and in the presence of a catalyst        effective for the methylation to produce a third product having        a higher xylenes content than said reformate.

The methylation reaction can occur in the liquid phase or the vaporphase. Usually the reaction will occur in the vapor phase. The presenceof the vapor phase in the reactor zone results in increased catalyticactivity in the reactor zone and increased diffusion of molecules to thecatalytic sites of the catalyst, e.g., pores of the molecular sieve. Theexpression “vapor phase”, as used herein, includes the presence of minoramounts of some liquid phase, e.g., less than 10 percent by volume ofliquid, as well as the substantial absence of liquid phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified process flow diagram, illustrating an embodimentof the invention.

FIG. 2 is a simplified process flow diagram, illustrating anotherembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The term “aromatization”, as used herein, shall mean the production ofaromatics comprising benzene, toluene, or mixtures thereof by theconversion of non-aromatic hydrocarbons to aromatic hydrocarbonscomprising benzene, toluene, or mixtures thereof. The term“aromatization”, as used herein, shall also include the production ofaromatics comprising benzene, toluene, or mixtures thereof by thecracking of heavy aromatic hydrocarbons to produce the aromatichydrocarbons comprising benzene, toluene, or mixtures. Examples ofaromatization processes include catalytic reforming of naphtha,dehydrocyclo-oligomerization of C₂-C₅ aliphatic hydrocarbons, steamcracking of hydrocarbons to produce aromatic hydrocarbons comprisingbenzene, toluene, or mixtures thereof, and the catalytic cracking ofhydrocarbons to produce aromatic hydrocarbons comprising benzene,toluene, or mixtures thereof

The term “reformate”, as used herein, shall mean the product produced by“aromatization”.

FIG. 1 illustrates an embodiment of the invention, in simplified form,where the C₆/C₇ fraction from the reformate is methylated in a reactionzone located outside the reforming loop. Referring to FIG. 1, naphtha isdirected via line 1 to heat exchanger 3 where the temperature of thenaphtha is elevated. The naphtha feed can be either naphtha alone or thenaphtha can be combined with toluene. Next, the heated naphtha is sentvia line 5 to reformer heater 7 which elevates the temperature of thefeed to a temperature suitable for reforming. After heating, the naphthais withdrawn via line 9 to aromatization reactor zone 11 where thenaphtha is reformed into aromatic products. Although only one reactorzone is shown, there can be more than one reactor zone. The reformate isthen withdrawn and sent via line 13 to heat exchanger 3. Heat exchanger3 cools the reformate and uses the heat recovered from the reformate toelevate the temperature of the naphtha supplied via line 1. Next, thereformate is withdrawn through line 15 to heat exchanger 17 to furthercool the reformate for separation of hydrogen from the product. Next,the cooled reformate is sent via line 19 to high pressure separator 21where hydrogen is recovered. Hydrogen is removed via line 23 and eitherrecycled back to the reforming unit or removed from the system via line25. Next, the product is sent via line 27 to separation block 28 wherelow pressure hydrogen, C⁴⁻ and C₅ are separated and removed from theproduct. The hydrogen and C⁴⁻ and C₅ hydrocarbons are then sent via line29 to oxygenate/water removal unit 30. After separation of oxygenatesand water, the hydrogen and C⁴⁻ and C₅ hydrocarbons are removed fromoxygenate/water removal unit 30 via line 31. The C₆₊ product, includingbenzene and toluene, is sent via line 32 to oxygenate/water removal unit33. After removal of the oxygenates and water, the C₆₊ product issupplied via line 34 to distillation column 35. The C₈₊ fraction isremoved from the bottom of distillation column 35 via line 37 andfurther separated and converted in xylene loop 39 to the desiredmolecules, e.g., para-xylene and other by-products. The C₆/C₇ fraction,including benzene and toluene, is removed from distillation column 35overhead via line 41. Next, either part or all of the C₆/C₇ fraction issupplied via line 43 to methylation reaction zone 45. If desired, astream of hydrocarbons comprised of benzene and/or toluene can be addedto the C₆/C₇ fraction. The methylation reaction can be carried out inthe vapor phase. When carried out in the vapor phase, the C₆/C₇ fractioncan be heated either before it enters the methylation reaction zone orafter it has entered the methylation reaction zone. The methylatingagent can be supplied to methylation reaction zone 45 via line 47. Also,hydrogen-containing gas can be supplied to methylation reaction zone 45via line 49. The methylating agent is preferably supplied to methylationreaction zone 45 through a plurality of feed points, e.g., 3-6 feedpoints. In methylation reaction zone 45, the toluene present in theC₆/C₇ fraction is methylated to form xylenes. Also, benzene present inthe C₆/C₇ fraction can be methylated to form toluene which, in turn, canbe methylated to form xylenes. The catalyst used in the methylationreaction zone 45 for the methylation can be any catalyst effective fortoluene or benzene methylation, e.g., catalyst that produces equilibriumamounts of para-xylene, or one that is selective to produce greater thanequilibrium amounts of a desired xylene isomer, e.g., para-xylene. Themethylated product is then sent via line 51 and mixed with the productin line 27 to separation block 29. After leaving separation block 29 vialine 33, the methylated product is processed in distillation column 35and then sent to xylene loop 39. Practicing the invention according tothis embodiment allows sharing of the low pressure separator, thebenzene/toluene recovery unit and xylenes recovery unit.

As shown in FIG. 1, the methylation reaction zone is located to receivethe C₆/C₇ fraction from distillation column 35. For some operations, itmay be particularly useful for the methylation reaction zone to belocated between high pressure separator 21 and separation block 29. Inthis configuration, the methylation reaction zone will receive part orall of the reformate in which a portion of hydrogen has been removed.After leaving the methylation reaction zone, the methylated product willbe sent to separation block 29 and further processed. Also, for someoperations, it may particularly useful for the methylation reaction zoneto be located between separation block 29 and distillation column 35. Inthis embodiment, the methylation reaction zone will receive at least aportion of the reformate in which at least a portion of the hydrogen,C⁶⁻, and C⁵⁻ have been removed. After leaving the methylation reactionzone, the methylated product is sent to separation block 29. and furtherprocessed.

FIG. 2 illustrates another embodiment of the invention, in simplifiedform, where the methylation reaction takes place outside the reformingloop. In this embodiment, at least a portion of the hydrogen and C₈₊fraction is removed from the reformate and then the resulting product issent to the toluene methylation unit. Referring to FIG. 2, naphtha isdirected via line 61 to heat exchanger 63 where the temperature of thenaphtha is elevated. The naphtha feed can be either naphtha alone or thenaphtha can be combined with toluene. Next, the heated naphtha is sentvia line 65 to reformer heater 67 which elevates the temperature of thefeed to a temperature suitable for reforming. After heating, the naphthais withdrawn via line 69 to aromatization reactor zone 71 where thenaphtha is reformed into aromatic products. Although only one reactorzone is shown, there can be more than one reactor zone. The reformate isthen withdrawn and sent via line 73 to heat exchanger 63. Heat exchanger63 cools the reformate and uses heat recovered from the reformate toelevate the temperature of the naphtha supplied via line 61. Next, thereformate is withdrawn through line 75 to heat exchanger 77 to furthercool the reformate for separation of hydrogen from the product. Next,the cooled reformate is sent via line 79 to high pressure separator 81where hydrogen is recovered. Hydrogen is removed via line 83 and eitherrecycled back to the reforming unit or removed from the system via line85. Next, the product is sent via line 87 to C₈₊ separator 89 where atleast a portion of the C₈₊ fraction is separated and removed. from thebottom of separator 89 and sent to distillation column 95 via lines 91.and 94. Any product not sent to separator 89 can be sent via line 88 toseparation block 102. The C⁷⁻ fraction is removed overhead fromseparator 89 and supplied via line 97 to methylation reaction zone 98.If desired, a stream of hydrocarbons comprised of benzene and/or toluenecan be added to the reformate. The methylation reaction can be carriedout in the vapor phase. When carried out in the vapor phase, the C⁷⁻fraction can be heated either before it enters the methylation reactionzone or after it has entered the methylation reaction zone. Themethylating agent can be supplied to methylation reaction zone 98 vialine 99. Also, hydrogen-containing gas can be supplied to methylationreaction zone 98 via line 100. The methylating agent is preferablysupplied to methylation reaction zone 98 through a plurality of feedpoints, e.g., 3-6 feed points. The methylated product is then sent vialine 101 to separation block 102 where low pressure hydrogen, C⁴⁻ and C₅are separated and removed from the product. The hydrogen and C⁴⁻ and C₅hydrocarbons removed via line 103 to oxygenate/water removal unit 104.After separation of oxygenates and water, the hydrogen and C⁴⁻ and C₅hydrocarbons are removed from oxygenate/water removal unit 104 via line105. The C₆₊ product, including benzene and toluene, is sent via line106 to oxygenate/water removal unit 107. The resulting product, C₆₊,including benzene and toluene, is supplied via line 109 and line 94 todistillation column 95. The C₈₊ fraction is removed from the bottom ofdistillation column 95 via line 111 and further separated and convertedin xylene loop 113 to the desired molecules, e.g., para-xylene and otherby-products. The C₆/C₇ fraction, including benzene and toluene, isremoved from distillation column 95 overhead via line 115. Practicingthe invention according to this embodiment allows sharing of the lowpressure separator, the benzene/toluene recovery unit and xylenesrecovery unit.

Aromatization

Aromatization will usually be carried out by catalytic reforming ofnaphtha or the dehydrocyclo-oligomerization of C₂-C₅ aliphatics.

Dehydrocyclo-oligomerization involves converting C₂-C₅ aliphatichydrocarbons to aromatic hydrocarbons. The process is carried out bycontacting C₂-C₅ aliphatic hydrocarbons in an aromatization zone and inthe presence of a catalyst suitable for dehydrocyclodimerization andunder conditions effective to produce a aromatics product comprisingbenzene and/or toluene. The dehydrocyclodimerization process increasescarbon chain length by oligomerization, promotes cyclization, anddehydrogenates cyclics to their respective aromatics.

The feedstream used in the dehydrocyclo-oligomerization process willcontain at least one aliphatic hydrocarbon containing 2 to about 5carbon atoms. The aliphatic hydrocarbons may be open chain, straightchain, or cyclic. Examples such as hydrocarbons include ethane,ethylene, propane, propylene, n-butane, n-butenes, isobutane, isobutene,butadiene, straight and branch pentane, pentene, and pentyldiene.Dehydrocyclo-oligomerization conditions. will vary depending on suchfactors as feedstock composition and desired conversion. A desired rangeof conditions for the dehydro-cyclodimerization of the aliphatichydrocarbons to aromatics include a temperature from about 350° to about650° C., a pressure from about 1 to about 100 atmospheres, and weighthour space velocity from about 0.2 to about 8. It is understood that, asthe average carbon number of the feed increases, a temperature in thelower end of temperature range is required for optimum performance andconversely, as the average carbon number of the feed decreases, thehigher the required reaction temperature.

The catalyst used in the dehydrocyclo-oligomerization reaction willpreferably comprise an intermediate pore size molecular sieve.Intermediate pore size molecular sieves have a pore size from about 5 toabout 7 Å and include, for example, AEL, AFI, MWW, MFI, MEL, MFS, MEI,MTW, EUO, MTT, HEU, FER, and TON structure type molecular sieves. Thesematerials are described in “Atlas of Zeolite Structure Types”, eds. W.H. Meier, D. H. Olson, and Ch. Baerlocher, Elsevier, Fourth Edition,1996, which is hereby incorporated by reference. Examples of suitableintermediate pore size molecular sieves include ZSM-5, ZSM-11, ZSM-12,ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, ZSM-57, MCM-22,MCM-49, MCM-56, and SAPO-5. Preferred molecular sieves are SAPO-11, aswell as titanosilicate, gallosilicate, aluminosilicate, andgallium-containing aluminosilicate molecular sieves having a MFIstructure.

Usually the molecular sieve will be combined with binder materialresistant to the temperature and other conditions employed in theprocess. Examples of suitable binder material include clays, alumina,silica, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The molecularsieve may also be composited with zeolitic material such as the zeoliticmaterials which are disclosed in U.S. Pat. No. 5,993,642, which ishereby incorporated by reference.

The relative proportions of molecular sieve and binder material willvary widely with the molecular sieve content ranging from between about1 to about 99 percent by weight, more preferably in the range of about10 to about 70 percent by weight of molecular sieve, and still morepreferably from about 20 to about 50 percent.

To make enhanced amounts (greater than equilibrium amounts) ofpara-xylene (versus the other xylene isomers produced by thedehydrocyclo-oligomerization reaction), a molecular sieve catalyst,e.g., ZSM-5 catalyst, can be selectivated by the use of a selectivatingagent.

Examples of compounds for selectivating the catalysts include treatingthe surface of the catalyst with compounds of phosphorus and/or variousmetal oxides such as alkaline earth metal oxides, e.g., calcium oxide,magnesium oxide, etc. rare earth metal oxides, lanthanum oxide, andother metal oxides such as boron oxide, titania, antimony oxide, andmanganese oxide.

Selectivation may also be accomplished by depositing coke on thecatalyst. The coke selectivation can be carried out during themethylation reaction such as by running the methylation reaction atconditions which allow the deposition of coke on the catalyst. Also, thecatalyst can be preselectivated with coke such as by exposing thecatalyst in the reactor to a thermally decomposable organic compound,e.g., benzene, toluene, etc. at a temperature in excess of thedecomposition temperature of said compound, e.g., from about 400° C. toabout 650° C., more preferably 425° C. to about 550° C., at a WHSV inthe range of from about 0.1 to about 20 lbs. of feed per pound ofcatalyst per hour, at a pressure in the range of from about 1 to about100 atmospheres, and in the presence of 0 to about 2 moles of hydrogen,more preferably from about 0.1 to about 1 moles of hydrogen per mole oforganic compound, and optionally in the presence of 0 to about 10 molesof nitrogen or another inert gas per mole of organic compound. Thisprocess is conducted for a period of time until a sufficient quantity ofcoke has deposited on the catalyst surface, generally at least about 2%by weight and more preferably from about 8 to about 40% by weight ofcoke.

Selectivation of the catalyst may also be accomplished usingorganosilicon compounds. The silicon compounds may comprise apolysiloxane include silicones, a siloxane, and a silane includingdisilanes and alkoxysilanes.

Silicone compounds that can be used in the present invention include thefollowing:

wherein R₁ is hydrogen, fluoride, hydroxy, alkyl, aralkyl, alkaryl orfluoro-alkyl. The hydrocarbon substituents generally contain from 1 toabout 10 carbon atoms and preferably are methyl or ethyl groups. R₂ isselected from the same group as R₁, and n is an integer of at least 2and generally in the range of 2 to about 1000. The molecular weight ofthe silicone compound employed is generally between about 80 to about20,000 and preferably about 150 to about 10,000. Representative siliconecompounds include dimethylsilicone, diethylsilicone,phenylmethylsilicone, methyl hydrogensilicone, ethylhydrogensilicone,phenylhydrogensilicone, fluoropropylsilicone,ethyltrifluoroprophysilicone, tetrachlorophenyl methylmethylethylsilicone, phenylethylsilicone, diphenylsilicone,methyltrisilicone, tetrachlorophenylethyl silicone, methylvinylsiliconeand ethylvinylsilicone. The silicone compound need not be linear but maybe cyclic as for example hexamethylcyclotrisiloxane,octamethylcyclotetrasiloxane, hexaphenyl cyclotrisiloxane andoctaphenylcyclotetrasiloxane. Mixtures of these compounds may also beused as well as silicones with other functional groups.

Useful siloxanes and polysiloxanes include as non-limiting examplehexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, octamethytrisiloxane,decamethyltetrasiloxane, hexaethylcyclotrisiloxane, octaethylcyclotetrasiloxane, hexaphenylcyclotrisiloxane andoctaphenylcyclo-tetrasiloxane.

Useful silanes, disilanes, or alkoxysilanes include organic substitutedsilanes having the general formula:

wherein R is a reactive group such as hydrogen, alkoxy, halogen,carboxy, amino, acetamide, trialkylsilyoxy, R₁, R₂ and R₃ can be thesame as R or can be an organic radical which may include alkyl of from 1to about 40 carbon atoms, alkyl or aryl carboxylic acid wherein theorganic portion of alkyl contains 1 to about 30 carbon atoms and thearyl group contains about 6 to about 24 carbons which may be furthersubstituted, alkylaryl and arylalkyl groups containing about 7 to about30 carbon atoms. Preferably, the alkyl group for an alkyl silane isbetween about 1 and about 4 carbon atoms in chain length. Mixtures mayalso be used.

The silanes or disilanes include, as non-limiting examples,dimethylphenylsilane, phenytrimethylsilane, triethylsilane andhexamethyldislane. Useful alkoxysilanes are those with at least onesilicon-hydrogen bond.

Selectivation of the catalyst can also be accomplished using acombination of coke and silicon applied by the procedures describedabove.

Catalytic reforming involves the production of aromatics from a C₆₊paraffinic feed, e.g., naphtha, by contacting the feed with a reformingcatalyst under reforming conditions to produce a reaction productcomprising aromatics and paraffins. The reformate is formed undertypical reforming conditions designed to promote dehydrogenation ofnaphthenes, isomerization of paraffinic hydrocarbons anddehydrocyclization of non-aromatic hydrocarbons.

Catalysts suitable for use in catalytic reforming include acidicreforming catalysts (bifunctional catalysts) and non-acidic reformingcatalysts (monofunctional catalysts).

Acidic reforming catalysts usually comprise a metallic oxide supporthaving disposed therein a Group VIII metal. Suitable metallic oxidesupports include alumina and silica. Preferably, the acidic reformingcatalyst comprises a metallic oxide support having disposed therein inintimate admixture a Group VIII metal (preferably platinum) and a metalpromoter, such as rhenium, tin, germanium, cobalt, nickel, iridium,rhodium, ruthenium and combinations thereof. More preferably, the acidicreforming catalyst comprises an alumina support, platinum, and rheniumor platinum and tin on an alumina support.

Non-acidic or monofunctional reforming catalysts will comprise anon-acidic molecular sieve, e.g., zeolite, and one or morehydrogenation/dehydrogenation components. Examples of suitable molecularsieves include MFI structure type, e.g., silicalite, and molecularsieves having a large pore size, e.g., pore size from about 7 to 9Angstroms. Examples of large pore molecular sieves include LTL, FAU, and*BEA structure types. Examples of specific molecular sieves includezeolite L, zeolite X, zeolite Beta, zeolite Y, and ETS-10.

The non-acidic catalysts will contain one or morehydrogenation/dehydrogenation metals, e.g., Group VII B metals, such asrhenium, and Group VIII metals, such as nickel, ruthenium, rhodium,palladium, iridium or platinum. The preferred Group VIII metal isplatinum. Also, the non-acidic catalysts can contain a metal promotersuch as tin.

The amount of hydrogenation/dehydrogenation metal present on thenon-acidic catalyst will usually be from about 0.1% to about 5% ofhydrogenation/dehydrogenation metal based on the weight of the catalyst.The metal can incorporated into the zeolite during synthesis of thezeolite, by impregnation, or by ion exchange of an aqueous solutioncontaining the appropriate salt. By way of example, in an ion exchangeprocess, platinum can be introduced by using cationic platinum complexessuch as tetraammine-platinum (II) nitrate.

The non-acidic catalyst will usually include a binder. The binder can bea natural or a synthetically produced inorganic oxide or combination ofinorganic oxides. Typical inorganic oxide supports which can be usedinclude clays, alumina, and silica, in which acidic sites are preferablyexchanged by cations that do not impart strong acidity.

The reforming process can be continuous, cyclic or semi-regenerative.The process can be in a fixed bed, moving bed, tubular, radial flow orfluid bed.

Conditions for reforming conditions include temperatures of at leastabout 400° C. to about 600° C. and pressures from about 50 psig (446kPa) to about 500 psig (3,549 kPa), a mole ratio of hydrogen tohydrocarbons from 1:1 to 10:1 and a liquid hour space velocity ofbetween 0.3 and 10.

Substantially any hydrocarbon feed containing C₆₊ e.g., naphtha can beutilized. The naphtha will generally comprise C₆-C₉ aliphatichydrocarbons. The aliphatic hydrocarbons may be straight or branchedchain acyclic hydrocarbons, and particulary paraffins such as heptane.

Toluene/Benzene Methylation

The methylation reaction can be carried out in vapor phase. Reactionconditions suitable for use in the present invention includetemperatures from about 300° C. to about 700° C. and preferably about400° C. to about 700° C. The reaction is preferably carried out at apressure from about 1 to 1000 psig, and a weight hourly space velocityof between about 0.1 and about 200 and preferably between about 1 andabout 100 weight of charge per weight of catalyst per hour. The molarratio of toluene and benzene to methylating agent can vary and willusually be from about 0.1:1 to about 20:1. Preferred ratios foroperation are in the range of 2:1 to about 4:1. Hydrogen gas can besupplied to the reaction as an anticoking agent and diluent. Themethylating agent is usually supplied to the methylation reaction zonethrough multiple feed points, e.g., 3-6 feed points.

Typical methylating agents include methanol, dimethylether,methylchloride, methylbromide, methylcarbonate, acetaldehyde,dimethoxyethane, acetone, and dimethylsulfide. The methylating agent canalso be formed from synthesis gas, e.g., the agent can be formed fromthe H₂, CO, and/or CO₂ of synthesis gas. The methylating agent can beformed from the synthesis gas within the methylation reaction zone. Oneskilled in the art will know that other methylating agents may beemployed to methylate the benzene and/or toluene based on thedescription provided therein. Preferred methylating agents are methanoland dimethylether. Methanol is most preferred.

Catalysts suitable for use in the present invention include any catalystthat is effective for toluene or benzene methylation. The catalyst usedin the process will usually comprise a crystalline molecular sieve.

The catalyst used in the methylation reaction will preferably comprisean intermediate pore size molecular sieve. Intermediate pore sizemolecular sieves have a pore size from about 5 to about 7 Å and include,for example, AEL, AFI, MWW, MFI, MEL, MFS, MEI, MTW, EUO, MTT, HEU, FER,and TON structure type zeolites. These materials are described in “Atlasof Zeolite Structure Types”, eds. W. H. Meier, D. H. Olson, and Ch.Baerlocher, Elsevier, Fourth Edition, 1996, which is hereby incorporatedby reference. Examples of suitable intermediate pore size molecularsieves include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-34, ZSM-35,ZSM-38, ZSM-48, ZSM-50, ZSM-57, MCM-22, MCM-49, MCM-56, and SAPO-5.Preferred molecular sieves are SAPO-11, as well as titanosilicate,gallosilicate, aluminosilicate, and gallium-containing aluminosilicatemolecular sieves having a MFI structure.

The intermediate pore size molecular sieve will generally be acomposition having the following molar relationship:X₂O₃:(n)YO₂wherein X is a trivalent element such as titanium, aluminum, iron,boron, and/or gallium and Y is a tetravalent element such as silicon,tin, and/or germanium; and n has a value greater than 12, said valuebeing dependent upon the particular type of molecular sieve. When theintermediate pore size molecular sieve is a MFI structure type molecularsieve, n is preferably greater than 10 and preferably, from 20:1 to200:1.

When the molecular sieve has a gallium silicate composition, themolecular sieve usually will be a composition having the following molarrelationship:Ga₂O₃:ySiO₂wherein y is between about 20 and about 500. The molecular sieveframework may contain only gallium and silicon atoms or may also containa combination of gallium, aluminum, and silicon.

Usually the molecular sieve will be incorporated with binder materialresistant to the temperature and other conditions employed in theprocess. Examples of suitable binder material include clays, alumina,silica, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, and silica-titania, as well as ternary compositions,such as silica-alumina-thoria, silica-alumina-zirconia,silica-alumina-magnesia and silica-magnesia-zirconia. The molecularsieve may also be composited with zeolitic material such as the zeoliticmaterials which are disclosed in U.S. Pat. No. 5,993,642.

The relative proportions of molecular sieve and binder material willvary widely with the molecular sieve content ranging from between about1 to about 99 percent by weight, more preferably in the range of about10 to about 70 percent by weight of molecular sieve, and still morepreferably from about 20 to about 50 percent.

The catalyst may also include at least one hydrogenation/dehydrogenationmetal. Such metals can reduce the rate of deactivation of the catalyst.Reference to hydrogenation/dehydrogenation metal or metals is intendedto encompass such metal or metals in the elemental state (i.e. zerovalent) or in some other catalytically active form such as an oxide,sulfide, halide, carboxylate and the like. Such metals are known topersons skilled in the art and include, for example, one or more metals,and metals of Groups IIIA, IVA, VA, VIA, VIIA, VIII, IB, IIB, IIIB, IVB,VB, VIB, and VIIB of the Periodic Table of the Elements. Examples ofsuitable metals include Group VIII metals (i.e., Pt. Pd, Ir, Rh, Os, Ru,Ni, Co and Fe), Group IVA metals (i.e., Sn and Pb), Group VA metals(i.e., Sb and Bi), and Group VIIB metals (i.e., Mn, Tc and Re). Noblemetals (i.e., Pt, Pd, Ir, Rh, Os and Ru) are sometimes preferred.

When the catalyst used for the methylation reaction is a molecularsieve, the catalyst can be selectivated to enhance the amount ofpara-xylene produced by the methylation reaction by the use of aselectivating agent. Suitable selectivating agents include theselectivating agents disclosed earlier in this application forselectivating dehydrocyclo-oligomerization molecular sieve catalysts.

Catalysts particularly suited for the methylation reaction are zeolitebound zeolite catalysts. These catalysts, as well as their method ofpreparation, are described in U.S. Pat. No. 5,994,603, which is herebyincorporated by reference. The zeolite bound zeolite catalysts willcomprise first crystals of an acidic intermediate pore size firstmolecular sieve and a binder comprising second crystals of a secondmolecular sieve. Preferably, the zeolite bound zeolite catalyst containsless than 10 percent by weight based on the total weight of the firstand second zeolite of non-zeolitic binder, e.g., amorphous binder. Anexample of such a catalyst comprises first crystals of a MFI or MELstructure type, e.g., ZSM-5 or ZSM-11, and a binder comprising secondcrystals of MFI or MEL structure type, e.g., Silicalite 1 or Silicalite2.

The amount of benzene/toluene converted to xylenes will depend on anumber of factors including the make up of the reformate to bemethylated, the methylation conditions, and the catalyst used. Usually,at least 5 weight percent of the benzene/toluene will be converted toxylenes. Preferably, at least 7 weight percent of the benzene/toluenewill be converted to xylenes, and, more preferably, at least 30 weightpercent of the benzene/toluene will be converted to xylenes.

Also, the process of this invention may be used to produce greater thanequilibrium amounts of para-xylene. Preferably, the process will producea xylene product containing greater than 30 weight percent para-xylenebased on the total weight of xylenes produced by the process. Morepreferably, the process produces a xylene product containing greaterthan 60 weight percent para-xylene based on the total weight of thexylenes produced by the process. Most preferably, the process produces axylene product containing greater than 80 weight percent para-xylenebased on the total weight of the xylenes produced by the process.

EXAMPLE 1

A simulated naphtha reformate feed (naphtha reformate without hydrogen,C₁-C₅ hydrocarbons, and C₈₊ hydrocarbons) was subjected to methylationusing a zeolite bound zeolite catalyst. The simulated feed had thecomposition given below in Table 1:

TABLE 1 Component Wt. % C⁵⁻ 0.00 n-C₆ 33.12 i-C₆ 3.69 n-C₇ 0.00 i-C₇0.00 Benzene 15.85 Toluene 47.35 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The catalyst used for the test comprised 70 wt. % H-ZSM-5 core crystals(average particle size of 3.5 microns) having a silica to alumina moleratio of 75:1 and 30 wt. % ZSM-5 binder crystals having a silica to moleratio of approximately 900:1. The catalyst was prepared by first mixingthe ZSM-5 core crystals with amorphous silica containing a trace amountof alumina and then extruding the mixture into a silica bound extrudate.Next, the silica binder of the extrudate was converted to the secondzeolite by aging the aggregate at elevated temperatures in an aqueoussolution containing a template and hydroxy ions sufficient to covert thesilica to the binder crystals. The resulting zeolite bound zeolite wasthen washed, dried, calcined, and ion exchanged into the hydrogen form.

The methylation was carried out under the conditions shown below inTable 2:

TABLE 8 Component WHSV (h⁻¹) 9.2 MeOH/:Toluene [molar] 0.37 H2:(MeOH +HCs) [molar] 2 Pressure (psig) 200 Temperature (° F.) 900

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen at reactortemperature range from room temperature to 950° F. for two hours. Next,the feed was introduced into the reactor and the test was carried out atthe conditions shown in Table 2. The results of the test are set forthbelow in Table 3.

TABLE 3 Component Wt. % C⁵⁻ 1.94 n-C₆ 31.88 i-C₆ 3.48 n-C₇ 0.00 i-C₇0.00 Benzene 14.38 Toluene 43.11 PX 4.12 MX 0.29 OX 0.10 EB 0.23 C₉₊0.46 Total 100

The results in Table 3 shows that after methylation, the content of thereformate increased from no xylenes being present to 4.51% xylenes.Also, the amount of para-xylene produced (91% para-xylene) was greaterthan equilibrium amounts (24% para-xylene).

EXAMPLE 2

A simulated light naphtha reformate feed was subjected to toluenemethylation. The catalyst used in the test comprised 1/16 inchextrudates which contained 65 weight percent H-ZSM-5 and 35 weightpercent silica binder. The catalyst had an alpha value of 330. The“alpha value” of a catalyst is an approximate indication of itscatalytic cracking activity. The alpha test is described in U.S. Pat.No. 3,354,078 and in the Journal of Catalysis, Vol. 4, 522-529 (1965);Vol. 6, 278 (1966); and Vol. 61, 395 (1980), each incorporated herein byreference to that description.

The reformate feed used in the test had the composition given below:

TABLE 4 Component Wt. % C⁵⁻ 0.00 n-C₆ 18.58 i-C₆ 15.04 n-C₇ 4.30 i-C₇5.37 Benzene 15.32 Toluene 41.38 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 5 Component WHSV ((h⁻¹) 1 MeOH/:Toluene [molar] 1 H2:(MeOH + HCs)[molar] 1 Pressure (psig) 64 Temperature (° F.) 700

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen at reactortemperature range from room temperature to 950° F. for two hours. Next,the reformate was introduced into the reactor and the test was carriedout under the conditions shown in Table 5. The results of the test areset forth below in Table 6.

TABLE 6 Component Wt. % C⁵⁻ 1.13 n-C₆ 16.58 i-C₆ 13.43 n-C₇ 3.87 i-C₇4.33 Benzene 11.06 Toluene 35.82 PX 2.59 MX 3.20 OX 3.76 EB 0.00 C₉₊4.23 Total 100

The results report in Table 6 shows that after toluene methylation, thecontent of the reformate increased from no xylenes being present to9.49% xylenes. Also, the amount of para-xylene produced (27%para-xylene) was greater than an equilibrium amount (24% para-xylene).

EXAMPLE 3

A simulated light reformate, which would be formed by thedehydrocyclo-oligomerization of C₂-C₅ aliphatic hydrocarbons, wassubjected to toluene methylation. The catalyst used in the test had analpha value of approximately 22 and comprised 1/16 inch extrudates whichcontained 65 wt. % H-ZSM-23 having a silica to alumina mole ratio of110:1 and 35 wt. % of alumina binder. The ZSM-23 was prepared accordingto U.S. Pat. No. 4,076,842.

The reformate feed used in the test had the composition given below:

TABLE 7 Component Wt. % C⁵⁻ 0.00 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 35.00 i-C₇5.00 Benzene 15.00 Toluene 45.00 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 8 Component WHSV (h⁻¹) 8 MeOH/:Toluene [molar] 1/3 H2:(MeOH + HCs)[molar] 2 Pressure (psig) 150 Temperature (° F.) 932

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen to the reactiontemperature. Next, the reformate was introduced into the reactor and thetest was run at the conditions shown in Table 8. The results of the testare set forth below in Table 9.

TABLE 9 Component Wt. % C⁵⁻ 19.25 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 16.10 i-C₇4.65 Benzene 13.07 Toluene 41.45 PX 2.74 MX 1.83 OX 0.91 EB 0.00 C₉₊0.00 Total 100

The results in Table 9 shows that after toluene methylation, the contentof the reformate increased from no xylenes being present to 5.48%xylenes. Also, the amount of para-xylene produced (50% para-xylene) wasgreater than an equilibrium amount (24% para-xylene).

EXAMPLE 4

A simulated light reformate, which would be formed by thedehydrocyclo-oligomerization of C₂-C₅ aliphatic hydrocarbons, wassubjected to toluene methylation using a SAPO-11 catalyst. The catalysthad an alpha value of approximately 52 and its chemical analysis wasSi_(0.1)Al_(0.46)P_(0.44). The SAPO-11 was prepared according to U.S.Pat. No. 6,294,493

The reformate feed used in the test had the composition given below:

TABLE 10 Component Wt. % C⁵⁻ 0.00 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 35.00 i-C₇5.00 Benzene 15.00 Toluene 45.00 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 11 Component WHSV (h⁻¹) 8 MeOH/:Toluene [molar] 1/3 H2:(MeOH +HCs) [molar] 2 Pressure (psig) 150 Temperature (° F.) 932

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen to the reactiontemperature. Next, the reformate was introduced into the reactor and thetest was run at the conditions shown in Table 11. The results of thetest are set forth below in Table 12.

TABLE 12 Component Wt. % C⁵⁻ 19.25 n-C₆ 0.00 i-C₆ 0.00 n-C₇ 16.10 i-C₇4.65 Benzene 13.07 Toluene 41.45 PX 2.74 MX 1.83 OX 0.91 EB 0.00 C₉₊0.00 Total 100

The results in Table 12 shows that after toluene methylation, thecontent of the reformate increased from no xylenes being present to 5.8%xylenes. Also, the amount of para-xylene produced >40% para-xylene, wasgreater than an equilibrium amount (24% para-xylene).

EXAMPLE 5

A simulated full range naphtha reformate (without C₁-C₅ hydrocarbons)was subjected to toluene methylation using a silica selectivatedH-ZSM-5/silica bound catalyst.

The catalyst was selectivated by contacting H-ZSM-5/silica bound (65weight % H-ZSM-5 35 weight % silica) with dimethylphenylmethylpolysiloxane dissolved in decane and subsequently calcining theselectivated catalyst. The catalyst was treated with 3 additionalsilicon selectivation treatments using substantially the same procedure.The catalyst had an alpha value of approximately 300.

The reformate feed used in the test had the composition given below:

TABLE 13 Component Wt. % C⁵⁻ 0.00 n-C₆ 33.12 i-C₆ 3.69 n-C₇ 0.00 i-C₇0.00 Benzene 15.85 Toluene 47.35 PX 0.00 MX 0.00 OX 0.00 EB 0.00 C₉₊0.00 Total 100

The test was carried out under the following conditions:

TABLE 14 Component WHSV (h⁻¹) 9.2 MeOH/:Toluene [molar] 0.37 H2:(MeOH +HCs) [molar] 2 Pressure (psig) 200 Temperature (° F.) 900

The test was carried out by loading the catalyst into a fixed bedreactor and heating the catalyst in flowing hydrogen at a reactortemperature range from room temperature to 950° F. for two hours. Next,the reformate was introduced into the reactor and the test was run atthe conditions shown in Table 14. The product contained more than 90%para-xylene based on the total amount of xylenes present in the product.

1. An process for producing xylenes from naphtha, which processcomprises the steps of: (a) aromatizing naphtha in an aromatization zoneunder aromatization conditions and the presence of a first catalysteffective for the aromatization of the naphtha to produce a reformatecontaining hydrogen, C₁-C₅ hydrocarbons, C₆-C₇ hydrocarbons comprisingbenzene, toluene or mixtures thereof, and C₈₊ hydrocarbons; (b) removingat least a portion of said hydrogen from said reformate to produce afirst product having less hydrogen content than said reformate; (c)removing at least a portion of said C₁-C₅ hydrocarbons from said firstproduct in a C₁-C₅ hydrocarbon separation zone to produce a secondproduct having less C₁-C₅ hydrocarbon content than said first product;(d) removing at least a portion of said C₈₊ hydrocarbons from saidsecond product in a C₈₊ hydrocarbon separation zone to produce a thirdproduct having less C₈₊ hydrocarbon content than said second product;(e) transferring at least a portion of said third product to amethylation reaction zone; and (f) methylating in said methylationreaction zone at least a portion of the benzene, toluene, or mixturesthereof present in said third product with a methylating agent undervapor phase conditions effective for the methylation and in the presenceof a second catalyst effective for the methylation to produce a fourthproduct having a higher xylenes content than said reformate, whereinsaid second catalyst comprises a zeolite-bound-zeolite catalyst, aselectivated zeolite, ZSM-23, or a mixture thereof, and wherein saidzeolite in said zeolite-bound-zeolite catalyst or said selectivatedzeolite comprises ZSM-5.
 2. The process recited in claim 1, furthercomprising the steps of: (a) transferring at least a portion of saidfourth product to said C₁-C₅ hydrocarbon separation zone and removingC₁-C₅ hydrocarbons from said fourth product to produce a fifth producthaving a lower C₁-C₅ content than said fourth product; (b) transferringat least a portion of said fifth product to said C₈₊ hydrocarbonseparation zone and removing C₈₊ hydrocarbons from said fifth product toproduce a sixth product; and (c) recovering xylenes from said sixthproduct.
 3. The process recited in claim 1, wherein said vapor phaseconditions effective for the methylation include a temperature fromabout 300° C. to about 700° C., a pressure from about 1 to 1000 psig, aweight hourly space velocity of between about 0.1 and about 200, a molarratio of methylating agent to toluene and benzene between about 0.1:1 toabout 20:1 and a weight hourly space velocity of between about 0.1 andabout
 200. 4. The process recited in claim 1, wherein said catalystfurther comprises at least one hydrogenation/dehydrogenation metal. 5.The process recited in claim 4, wherein said at least onehydrogenation/dehydrogenation metal is a Group VIII metal.
 6. Theprocess recited in claim 1, wherein said molecular sieve furthercomprises a selectivating agent.
 7. The process recited in claim 6,wherein said a selectivating agent is selected from the group consistingof silica, coke, phosphorus, alkaline earth metal oxides, rare earthmetal oxides, lanthanum oxide, boron oxide, titania, antimony oxide,manganese oxide, and mixtures thereof.
 8. The process recited in claim7, wherein said fourth product contains greater than 60 weight percentof para-xylene based on the total weight of the xylenes produced in saidmethylation reaction zone by the methylation said benzene, toluene, ormixtures thereof.
 9. The process recited in claim 1, wherein saidmethylating agent is selected from the group consisting of methanol,dimethylether, methylchloride, methylbromide, methylcarbonate,acetaldehyde, dimethoxyethane, acetone, and dimethylsulfide.
 10. Theprocess recited in claim 1, wherein the catalyst effective for saidaromatization is a bifunctional catalyst.
 11. The process recited inclaim 1, wherein the catalyst effective for said aromatization is amonofunctional catalyst.
 12. The process recited in claim 1, wherein atleast 7 weight percent of the benzene and/or toluene present in saidreformate is converted to xylenes.
 13. The process recited in claim 1,wherein said fourth product contains greater than equilibrium amountspara-xylene.
 14. An integrated process for producing xylenes fromnaphtha which process comprises the steps of: (a) aromatizing naphtha inan aromatization zone under aromatization conditions and the presence ofa first catalyst effective for the aromatization of the naphtha toproduce a reformate containing hydrogen, C₁-C₅ hydrocarbons, C₆-C₇hydrocarbons comprising benzene, toluene or mixtures thereof, and C₈₊hydrocarbons; (b) removing at least a portion of said hydrogen from saidreformate to produce a first product having less hydrogen content thansaid reformate; (c) removing at least a portion of said C₈₊ hydrocarbonsfrom said first product in a C₈₊ hydrocarbon separation zone to producea second product having less C₈₊ hydrocarbon content than said firstproduct; (d) transferring at least a portion of said second product to amethylation reaction zone; and, (e) methylating in said methylationreaction zone at least a portion of the benzene, toluene, or mixturesthereof present in said second with a methylating agent under conditionseffective for the methylation and in the presence of a second catalysteffective for the methylation to produce a third product having a higherxylenes content than said reformate, wherein said second catalystcomprises a zeolite-bound-zeolite catalyst, a selectivated zeolite,ZSM-23, or a mixture thereof, and wherein said zeolite in saidzeolite-bound-zeolite catalyst or said selectivated zeolite comprisesZSM-5.
 15. The process recited in claim 14, further comprising the stepsof: (a) transferring at least a portion of said third product to a C₁-C₅hydrocarbon separation zone and removing at least a portion of the C₁-C₅hydrocarbons from said third product to produce a fourth product havinga lower C₁-C₅ content than said third product; (b) transferring at leasta portion of said fourth product to a C₈₊ hydrocarbon separation zoneand removing C₈₊ hydrocarbons from said fourth product to produce afifth product; and (c) recovering xylenes from said fifth product. 16.The process recited in claim 14, wherein the conditions effective forthe methylation include a temperature from about 300° C. to about 700°C., a pressure from about 1 to 1000 psig, a weight hourly space velocityof between about 0.1 and about 200, a molar ratio of methylating agentto toluene and benzene between about 0.1:1 to about 20:1 and a weighthourly space velocity of between about 0.1 and about
 200. 17. Theprocess recited in claim 14, wherein said methylation is carried out inthe vapor phase.
 18. The process recited in claim 14, wherein saidcatalyst further comprises at least one hydrogenation/dehydrogenationmetal.
 19. The process recited in claim 18, wherein said at least onehydrogenation/dehydrogenation metal is a Group VIII metal.
 20. Theprocess recited in claim 14, wherein said molecular sieve furthercomprises a selectivating agent.
 21. The process recited in claim 20,wherein said a selectivating agent is selected from the group consistingof silica, coke, phosphorus, alkaline earth metal oxides, rare earthmetal oxides, lanthanum oxide, boron oxide, titania, antimony oxide,manganese oxide, and mixtures thereof.
 22. The process recited in claim20, wherein said third product contains greater than 30 weight percentof para-xylene based on the total weight of the xylenes produced in saidmethylation reaction zone by the methylation of said benzene, toluene,or mixtures thereof.
 23. The process recited in claim 20, wherein thethird product contains greater than 60 weight percent of para-xylenebased on the total weight of the xylenes produced in said methylationreaction zone by the methylation of said benzene, toluene, or mixturesthereof.
 24. The process recited in claim 14, wherein the catalysteffective for said aromatization is a bifunctional catalyst.
 25. Theprocess recited in claim 14, wherein the catalyst effective for saidaromatization is a monofunctional catalyst.
 26. The process recited inclaim 14, wherein at least 7 weight percent of the benzene and/ortoluene present in said reformate is converted to xylenes.